1. Field of the Invention
The present invention relates to the technology field of angle encoders, and more particularly to a precision calibration method for high-precise rotary encoder.
2. Description of the Prior Art
During Second World War, magnetic angle encoders are developed and applied in tanks for facilitating the gun turret of the tank able to rotate by a precise angle under any harsh environments. Furthermore, with the development of science and technology, optical angle encoders are subsequently proposed.
Recently, the angle encoders have been fully developed. Please refer to FIG. 1, which illustrates a schematic framework view of an absolute positioning circular grating. As shown in FIG. 1, the absolute positioning circular grating 1′ is developed and proposed by HEIDENHAIN and mainly consists of an inner annular grating 11′ and an outer annular grating 12′. In which, the outer annular grating 12′ and the inner annular grating 11′ are designed to an equal spacing grating and an unequal spacing grating, respectively. Thus, by such grating arrangement, the absolute positioning circular grating 1′ is able to carry out a precise and absolute angle coordinate with the use of multiple optical sensors.
Continuously referring to FIG. 2, where an arrangement diagram of the multiple optical sensors is shown. As shown in FIG. 2, eight equal angle position sensors 21′ are respectively disposed at the positions of eight circular points, and eight unequal angle position sensors 22′ are respectively disposed at the positions of eight triangular points. By such arrangement, when the absolute positioning circular grating 1′ is rotated by a constant speed, the angle position information of the outer annular grating 12′ and the inner annular grating 11′ would be accessed by the equal angle position sensors 21′ and the unequal angle position sensors 22′, such that the precise and absolute angle coordinate of the absolute positioning circular grating 1′ can be carried out after a complex cross-matching and calculation for the angle position information of the outer annular grating 12′ and the inner annular grating 11′ is completed.
Circular angle encoder having barcode proposed by ReniShaw is another optical angle encoder having been widely applied. Please refer to FIG. 3, which illustrates a schematic framework view of the circular angle encoder proposed by ReniShaw. As shown in FIG. 3, a barcode 22″ consisting of a plurality of bright and dark patterns is formed on the circumferential surface 21″ of circular angle encoder 2″. Therefore, after accessing the bright and dark patterns of the barcode 22″, it is able to obtain a high-precise angle coordinate of the circular angle coder 2″ through graphical comparison.
Although the absolute positioning circular grating 1′ developed by HEIDENHAIN and the circular angle encoder 2″ proposed by ReniShaw has been widely applied, inventors of the present invention find that these two angel encoders still include following drawbacks and shortcomings:
(1) As FIG. 1 shows, because the inner annular grating 11′ and the outer annular grating 12′ are formed on a circular disk by using tool machining, it is able to know that the absolute positioning circular grating 1′ naturally includes the drawback of graduation error. On the other hand, when the said absolute positioning circular grating 1′ is connected to the center rotary shaft of a work equipment for practical application, the drawbacks of scanning error and eccentric error would be produced after the absolute positioning circular grating 1′ has been long-term used. Wherein the scanning error is resulted from the dirty and/or damages of the inner annular grating 11′ and the outer annular grating 12′, and the long-term rotating friction between the circular disk of the absolute positioning circular grating 1′ and the center rotary shaft of the work equipment causes the production of the eccentric error.
(2) As FIG. 3 shows, since the barcode 22′ consisting of bright and dark patterns are formed on the circumferential surface 21″ of the circular angle encoder 2″ through tool machining or etching process, it is able to know that the circular angle encoder 2″ also naturally includes the drawback of graduation error. Moreover, when the said circular angle encoder 2″ is connected to the center rotary shaft of a work equipment for practical application, the drawbacks of scanning error and eccentric error would be produced after the circular angle encoder 2″ has been long-term used. Wherein the scanning error is resulted from the dirty and/or damages of the barcode 22″, and the long-term rotating friction between the circular angle encoder 2″ and the center rotary shaft of the work equipment causes the production of the eccentric error.
Accordingly, in view of the absolute positioning circular grating 1′ developed by HEIDENHAIN and the circular angle encoder 2″ proposed by ReniShaw reveal many practically-used drawbacks, the inventor of the present application has made great efforts to make inventive research thereon and eventually provided a precision calibration method for high-precise rotary encoder.